1. Field of the Invention
The present invention relates to an image heating apparatus suitable as a heat fixing apparatus for passing an unfixed toner image formed and born on a recording material (transferring material/printing sheet/photosensitive paper/electrostatic recording sheet) by using a transferring system or a direct system in an image forming process part through a heating nip part which is a crimping part of a heating member and a pressure member to heat-fix it as a fixed image on the recording material in an image forming apparatus such as a copying machine or a laser beam printer.
2. Description of Related Art
Conventionally, in an image forming apparatus which employs an electrophotographic system or the like, the heat fixing apparatus of a so-called heating roller system has widely been used, which passes a recoding material bearing an unfixed toner image through a heating nip part (fixing nip part) formed by pressure contact between a fixing roller as a heating member and a pressure roller as a pressure member which are pressed into contact with each other to rotate to heat-fix the image.
In the heat fixing apparatus of the heating roller system, the fixing roller as the heating member uses radiant heat from a halogen lamp disposed in the hollow core metal of heated aluminum to carry out heating which is sufficient to melt toner on the recording material from the inside of the core metal. In order to provide mechanical strength to the hollow core metal, a thickness of about 0.5 mm to 4.0 mm is necessary, and a large heat capacity is provided. Thus, it is necessary to preheat the fixing roller to a predetermined temperature during standby.
Additionally, an example of the heat fixing method of a film heating system has been presented and put into practical use, which supplies no power to a heat fixing apparatus especially during standby, and has good quick starting and energy-saving characteristics.
That is, a heat-resistant thin resin film (referred to as fixing film, hereinafter) is held between a ceramic heater which uses alumina, an aluminum nitride or the like for a substrate and a pressure roller to form a pressure contact nip part (fixing nip part), and introduces a recording material on which an unfixed toner image is formed and born between the fixing film and the pressure roller to hold and convey it together with the fixing film. The heat energy of the ceramic heater is supplied through the fixing film to the recording material, and the pressure force of the fixing nip part is received to fix the unfixed toner image on the recording material.
Various image forming apparatus such as a printer and a copying machine which use the fixing apparatus of such a film heating system have many advantages over the conventional system for heat-fixing the image by using the heating roller or the like, e.g., nonnecessity of preheating during standby, shortening of wait time etc., because of high heating efficiency and quick rising.
FIG. 8 is a schematic view showing the constitution of a heat fixing apparatus which uses a resin fixing film in a longitudinal direction. A reference numeral 10 denotes a fixing member assembly as a heating member. This assembly 10 comprises a heater 11 such as a ceramic heater which uses alumina, an aluminum nitride or the like for a substrate, a heat insulating stay holder 12 which holds the heater 11 on its bottom surface side, a cylindrical resin fixing film 43 loosely fitted to the heat insulating stay holder 12, film end regulating flanges 45 stuck to the heat insulating stay holder 12 to be arranged on both left and right end sides of the fixing film 43, etc.
In the film end regulating flange 45, a reference numeral 45a denotes a spring bearing seat part disposed on the outer surface side of the flange 45 to integrally project, and 45b denotes a film end support part disposed on the inner surface side of the flange 45 to integrally project. The film end support part 45b is inserted into a film end and positioned to support the film end from the inside.
A reference numeral 20 denotes a heat-resistant/elastic pressure roller as a pressure member. The pressure roller 20 comprises a core metal 21 and an elastic layer 22, and both ends of the core metal 21 are born and held to freely rotate between the left and right side plates of a not-shown apparatus chassis. A reference numeral 25 denotes a pressure roller rotary-driving gear secured to one end side of the pressure roller core metal.
The fixing member assembly 10 is arranged in parallel with the pressure roller 20 with the heater 11 side set downward to be mounted on the upper side of the pressure roller 20, and the spring bearing seat parts 45a of the film end regulating flanges 45 on both left and right end sides are pressed by the predetermined pressing forces of pressure springs 16 to apply pressure to the entire fixing member assembly 10 against the elasticity of the pressure roller 20.
Thus, the downward surface of the heater 11 is pressed into contact with the upper surface of the pressure roller 20 against the elasticity of the pressure roller 20 while the fixing roller 43 is held therebetween to form the fixing nip part N of a predetermined width between the fixing film 43 and the pressure roller 20. At the fixing nip N, the fixing film 43 is held between the heater 11 and the pressure roller 20 by a pressure force to be distorted, and bonded to the heating surface of the heater 11.
A driving force is transmitted from a not-shown driving system through a driving gear 25 to the pressure roller 20 to rotary-drive it. Upon the rotary-driving of the pressure roller 20, a friction force at the fixing nip part N drives the cylindrical fixing film 43 to rotate around the heat insulating stay holder 12 while its inner surface is slid in close contact with the downward surface of the heater 11 at the fixing nip N. Power is supplied to the heater 11 to generate heat, and a temperature is controlled to a predetermined fixing temperature. In a state in which the pressure roller 29 is rotary-driven, the fixing film 43 is then driven to rotate, and the temperature of the heater 11 is controlled to the predetermined fixing temperature, a recording material on which an unfixed toner image has been formed and born is introduced to the fixing nip part which is a pressure contact part between the fixing film 43 and the pressure roller 20. The recording material is held and conveyed on the fixing nip part N, the heat energy of the heater 11 is supplied through the fixing film 43 to the recording material, and the unfixed toner image receives a pressure force at the fixing nip part N to be fixed on the recording material surface by heat pressure.
When pressure forces are imbalanced in the left and right of a longitudinal direction due to variance in component tolerance or the like, or because of a difference in the outer diameter shape of the cylindrical fixing film, an uneven thickness in the longitudinal direction or the like, the cylindrical fixing film 43 receives a lopsided force in a thrust direction during a rotary operation to move either left or right. In order to regulate the lopsided force in the thrust direction, a constitution is necessary in which the end surface of the cylindrical fixing film 43 is abutted on a regulating member such as a flange member to be regulated. The film end regulating flange 45 is a regulating member such as a flange member to be regulated. The film end regulating flange 45 is a regulating member for this purpose. Even if a lopsided movement phenomenon occurs in the thrust direction (fixing film longitudinal direction), i.e., in the longitudinal left and right direction of the heater 11 or the heat insulating stay holder 12, int eh rotated state of the cylindrical fixing film 43 which is driven to rotate upon the rotary-driving of the pressure roller 20, the left end surface or the right end surface of the fixing film 43 is received by the inner surface of the film end regulating flange 45 of its side to regulate the lopsided movement.
In the heat fixing apparatus of the film heating system, if a metal thin sleeve formed by using a highly heat conductive metal for a base layer is used as a fixing film in place of the resin fixing film, fixing performance is enhanced to sufficiently deal with the high speed of the image forming apparatus.
However, in the heat fixing apparatus of the film heating system, if the highly heat conductive metal sleeve is used in place of the resin fixing film for the purpose of increasing heat conductivity, the following problems are inherent.
That is, if the end regulating flange 45 of the shape shown in FIG. 8 is used as the end regulating flange of the metal sleeve, the end of the metal sleeve is supported from the inner surface by the flange. When the sleeve moves to one side to be abutted on the flange during the rotary operation, the end surface of the metal sleeve receives an external force to expand its end outer diameter in a horn shape. If a lopsided force to the longitudinal end is strong, horn-shaped deformation becomes more conspicuous, and sliding friction between the sleeve end surface and the flange or bending fatigue at the fixing nip part causes end fissures or damage.
In order to prevent such a problem, the base layer of the metal sleeve may be formed thick to increase a tearing force. However, this is not preferable because a heat capacity is enlarged to delay rising time before the predetermined temperature of the heater.
Additionally, when the sleeve is thick, elastic deformation for bonding the metal sleeve to the heater surface becomes difficult, which makes it difficult to obtain a fixing nip width necessary for heat-fixing.
Thus, in order to prevent the horn-shaped expansion caused by the abutment on the end regulating flange while the metal sleeve is maintained thin, as shown in FIG. 9, FIGS. 10A and 10B, it is necessary to use the end regulating flange 15 which is constituted to be brought into contact with the outer surface of the metal sleeve 13, and to apply stress in the inner surface direction of the metal sleeve 13 with respect to a lopsided force.
The end regulating flange 15 shown in FIG. 9, FIGS. 10A and 10B is an outer bearing type flange which has a spring bearing seat part 15a disposed on the flange outer surface side to integrally project, and a chipped annular guard part 15b disposed on the flange inner surface to integrally project. The spring bearing seat part 15a receives the pressure spring 16 as in the case of the spring bearing seat part 45 of the end regulating flange 45 in FIG. 8. The chipped annular guard part 15b receives the end of the metal sleeve 13 on its inner side, and the inner surface of the chipped annular guard part 15b is brought into contact with the end outer surface of the metal sleeve, whereby the swelling of the metal sleeve in an outer surface direction is regulated with respect to the movement of the metal sleeve in the longitudinal direction. Other apparatus components are similar to those of the apparatus shown in FIG. 8.
However, even if the end regulating flange 15 of such an outer bearing type, the following problems are inherent.
That is, at the end regulating flange 15 of the outer bearing type, the outer peripheral surface of the end of the metal sleeve 13 and the inner surface of the chipped annular guard part 15b of the end regulating flange are slid to rub each other. The metal sleeve 13 is driven to rotate by friction with the pressure roller 20. However, when a friction force between the outer surface of the sleeve and the end regulating flange becomes larger due to the termination of durability or the like, the problems of an increase in the driving torque of the pressure roller 20, uneven rotation, even stick slippage at the worst etc., occur to disturb a fixed image or the conveying performance of the recording material.
Yet another problem is that when the metal sleeve 13 is moved to one side, the end surface of the sleeve and the abutment surface of the end regulating flange 15 are slid to rub each other. In most cases, the end regulating flange 15 is made of an insulating and heat-resistant resin normally for the purpose of blocking the heat of the heater and preventing current leakage caused by a bias applied to the sleeve as offset countermeasures. Accordingly, when the sharp end surface of the metal sleeve and the resin flange are slid to rub each other, the resin is scrape by the metal to generate friction powders, whereby a groove is formed on the abutment surface. If there are flashes or steps on the end surface of the metal sleeve 15, the resin scraping by the end surface of the sleeve progresses much more. Consequently, not only the driving torque is increased but also fissures or destruction occurs on the end surface of the metal sleeve.